Lubricant generally contains base oil and various additives. As the base oil, there are mentioned mineral oils to be obtained from crude oil, as well as ester-base oils, fluoro-base oils, poly-α-olefin oils and the like to be chemically synthesized. Of those, ester-base oils are favorably used for engine oils for jet planes and automobiles, and for greases, etc., as having a low pour point, a high viscosity index, a high ignition point, good lubrication performance and biodegradability, etc.
As ester-base oils, there are disclosed various types of esters, such as monoesters to be obtained through reaction of an aliphatic monocarboxylic acid and a monoalcohol; diesters to be obtained through reaction of aliphatic dibasic acid and monoalcohol; esters to be obtained through reaction of polyalcohol and aliphatic carboxylic acid; complex esters to be obtained through reaction of polyol, polybasic acid and aliphatic monocarboxylic acid; etc. (Patent References 1 to 5).
On the other hand, disclosed is a complex alcohol ester obtained from polyol, polybasic acid or its anhydride and polyalcohol, which is said to have excellent lubricity and biodegradability (Patent References 6 to 9). These patent publications have no other substantial description relating to polyalcohol than one relating to alkyl alcohol. In addition, the patent publications say that the product obtained through reaction of the above-mentioned materials contains a polybasic acid ester and a heavy component, but suggest that removing the polybasic acid ester through stripping to give a lubricant oil of high-viscosity heavy component is preferred. The patent publications do not describe detailed analysis of these products.